For example, the conductive polymer has such a high conductivity that it is used as a solid electrolyte of solid electrolyte capacitors such as in tantalum solid electrolyte capacitors, aluminum solid electrolyte capacitors, and niobium solid electrolyte capacitors.
For example, the conductive polymers used in such application can be obtained by means of chemical oxidation polymerization or electrolytic oxidation polymerization of thiophene or its derivatives.
As a dopant, an organic sulfonic acid can be mainly used to carry out chemical oxidation polymerization of thiophene or its derivative as mentioned above. In particular, it is said that an aromatic sulfonic acid is suitable. As an oxidant, a transition metal is used. In particular, it is said that ferric one is suitable. Usually, a ferric salt of aromatic sulfonic acid can be used to serve as a dopant and oxidant upon the chemical oxidation polymerization of thiophene or its derivative.
Also, among the ferric salts of aromatic sulfonic acid, it was reported as follows: Particularly useful is ferric toluenesulfonate or ferric methoxybenzene sulfonate. In order to synthesize a conductive polymer using them, they are used as a dopant and oxidant and mixed with a polymerizable monomer such as thiophene or its derivatives. These processes are simple and suitable for industrialization (see patent reference No. 1, and patent reference No. 2).
However, the requests to improving the capacitor characteristics become higher and higher. There was a problem that a solid electrolyte capacitor only using the conductive polymer above as an electrolyte could not fully satisfy those requests.
Then, there was proposed an electrolyte capacitor using both a solid electrolyte of a conductive polymer, and electrolyte liquid (Patent Reference No. 3).
In such an electrolyte capacitor using the electrolyte liquid as explained above, a solution is used as an electrolyte liquid which dissolves ammonium dicarboxylates such as ammonium adipate in a solvent such as ethylene glycol. However, the electrolyte capacitor using a conductive polymer together with an electrolyte liquid could have improved characteristics compared with an electrolyte capacitor only using a conductive polymer as an electrolyte, but it still could not accomplish an electrolyte capacitor with a high performance as desired.